1. Field of the Invention
The present invention relates to a method used in a wireless communications system and related communication device, and more particularly, to a method of handling Semi-Persistent Scheduling (SPS) Cell Radio Network Temporary Identifier (C-RNTI) in a wireless communication system and related communication device.
2. Description of the Prior Art
A long-term evolution (LTE) system, initiated by the third generation partnership project (3GPP), is now being regarded as a new radio interface and radio network architecture that provides a high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, an evolved universal terrestrial radio access network (E-UTRAN) includes a plurality of evolved Node-Bs (eNBs) and communicates with a plurality of mobile stations, also referred as to user equipments (UEs).
A long term evolution-advanced (LTE-A) system, as its name implies, is an evolution of the LTE system. The LTE-A system targets faster switching between power states, improves performance at a cell edge, and includes subjects, such as bandwidth extension, coordinated multipoint transmission/reception (CoMP), UL multiple-input multiple-output (MIMO), etc.
For bandwidth extension, carrier aggregation is introduced to the LTE-A system by which two or more component carriers are aggregated to achieve a wider-band transmission. Accordingly, the LTE-A system can support a wider bandwidth up to 100 MHz by aggregating a maximum number of 5 component carriers, where bandwidth of each component carrier is 20 MHz and is backward compatible with 3GPP Rel-8. An LTE-A specification supports carrier aggregation for both continuous and non-continuous component carriers with each component carrier limited to a maximum of 110 resource blocks. The carrier aggregation increases a bandwidth flexibility by aggregating the non-continuous component carriers. A component carrier is used as an UL component carrier or a downlink (DL) component carrier. Further, there is a one-to-one correspondence between the UL component carrier and the DL component carrier, i.e., each UL component carrier is paired with a corresponding DL component carrier. In an LTE-A time-division duplex (TDD) system, the UL component carrier and DL component carrier are the same component carrier.
When the UE is configured with the carrier aggregation (CA), the UE is allowed to receive and transmit data on one or multiple component carriers to increase the data rate. In the LTE-A system, it is possible for the eNB to configure the UE different numbers of UL and DL component carriers which depend on UL and DL aggregation capabilities, respectively. Moreover, the component carriers configured to the UE necessarily consists of one DL primary component carrier (PCC) and one UL primary component carrier. Component carriers other than the primary component carriers are named UL or DL secondary component carriers (SCCs). The numbers of UL and DL secondary component carriers are arbitrary, and are related to the UE capability and available radio resource. In carrier aggregation, the UE only has one RRC connection with the network. At RRC connection establishment/re-establishment/handover, one serving cell provides the NAS mobility information, and at RRC connection re-establishment/handover, one serving cell provides the security input. This serving cell is referred to as the Primary Cell (PCell). In the downlink, the carrier corresponding to the PCell is the Downlink Primary Component Carrier (DL PCC) while in the uplink it is the Uplink Primary Component Carrier (UL PCC). The PCell can not be de-activated, but can be changed by a handover procedure.
Under such a configuration, semi-persistent downlink resources can only be configured for the primary component carrier. Similarly as for the downlink, semi-persistent uplink resources can only be configured for the primary component carrier. Therefore, when the UE receives an SPS uplink or downlink information (i.e. a downlink assignment or uplink grant), the UE determines a Physical Downlink Control Channel (PDCCH) validation process for the SPS information is valid if all the following conditions are met:                (a) The CRC parity bits obtained for the PDCCH payload are scrambled with the Semi-Persistent Scheduling C-RNTI; and        (b) The new data indicator field is set to ‘0’. In case of DCI formats 2, 2A and 2B, the new data indicator field refers to the one for the enabled transport block.        
After the UE determines the PDCCH validation process is valid in a physical (PHY) layer of the UE, the PHY layer delivers the Semi-Persistent Scheduling information to a Medium Access Control (MAC) layer of the UE for processing the downlink or uplink information and following operations.
However, in order to resolve the C-RNTI shortage issue by reusing a same Semi-Persistent Scheduling C-RNTI in different component carriers, an eNB may assign the same Semi-Persistent Scheduling C-RNTI to at least two UEs having different primary cells (PCells). In other words, the Semi-Persistent Scheduling C-RNTI is unique in a component carrier only. For example, a UE1 has a first PCell corresponding to a component carrier CC1 and another UE2 has a second PCell corresponding to another component carrier CC2. The UE1 and UE2 can be configured the same Semi-Persistent Scheduling C-RNTI.
Under such a situation, the UE configured with semi-persistent uplink or downlink resources and multiple component carriers (i.e. one primary component carrier and at least one secondary component carrier) may receive a downlink assignment or uplink grant with Semi-Persistent Scheduling C-RNTI and the downlink assignment or uplink grant allocates downlink or uplink resources on a secondary component carrier (i.e. corresponding to a SCell). According to the current prior art, the UE processes the downlink or uplink resources. However this causes a serious issue because the UE uses the downlink or uplink resources which may be allocated for another UE, which is configured the same Semi-Persistent Scheduling C-RNTI and the secondary component carrier of the UE as a primary component carrier.